from Western Australia. 389 



(peripheral). Test ornamented with ventrally-proj acted, subarcuate ribs, which (in 

 the cast) are inconspicuous on the inner third of the whorl. The inner whorls are 

 marked by forwardly inclined ribs, which (in the cast) are not very conspicuous on 

 the inner area, though they appear occasionally to have crossed this area. 



Dimensions : — 



Diameter of shell ....(estimated) about 60 mm. 



Height of outer whorl 19 )> 



Thickness of outer whorl 13'5 ,, 



"Width of umbilicus (estimated) about 26 ,, 



BemarTcs. — This species is represented by a single specimen con- 

 sisting of portions of three whorls of a shell about 60 mm. in 

 diameter. The whole is septate and only a small portion of the 

 test is preserved. The extreme length of the specimen along the 

 periphery is 71 mm. At the central point the dimensions of the 

 whorls are as follows : — • 



Height (breadth) of outer whorl 16-5 mm. 



Thickness of outer whorl H'o >> 



Height (breadth) of preceding whorl (as seen in a lateral aspect) ' J'O ,, 



Thickness of preceding whorl 7'5 ,, 



Height (breadth) of next inner whorl (as seen in a lateral aspect) 3-0 ,, 



Thickness of next inner whorl 4-5 ,, 



Thus the combined height (breadth) of the three adjacent whorls is seen 

 to be 26 '5 mm. 

 The specimen figured by Moore under the name Ammonites radians 

 most probably belongs to the present species. It has a diameter of 

 about 60 mm., but, for the sake of comparison with the example just 

 mentioned, the following measurements were taken at a point where 

 the shell has a radius of 28 mm. : — 



Height (breadth) of outer whorl 17 ^ mm. 



Thickness of outer whorl 10'£> m 



Umbilicus of outer whorl 21 ,, 



Height (breadth) of preceding whorl (as seen in a lateral aspect) 7 ,, 



Thickness of preceding whorl indeterminable 



Umbilicus of preceding whorl 9 mm. 



Height (breadth) of 2nd inner whorl (as seen in a lateral aspect) 2-5 ,, 



Thickness of 2nd inner whorl indeterminable 



Umbilicus of 2nd inner whorl 4 mm. 



Height (breadth) of 3rd inner whorl 1 >) 



It will thus be seen that at this point the combined height of 

 the outer and two earlier whorls is the same as in the previous 

 specimen, and that the relative proportion of the height of the whorls 

 is almost identical with that in the incomplete specimen previously 

 referred to. At the point where the septa are best seen, Moore's 

 specimen is somewhat abraded, so that the true form of the suture- 

 line is not displayed (see PI. XII. Fig. 3). 



Afflnities and differences. — This species at once suggests a com- 

 parison with Grammoceras, Hyatt, and Dumortieria, Haug ; both the 

 character of the ornamentation and the general form of the suture- 

 line suggest the division Grammoceras rather than Dumortieria. Mr. 

 S. S. Buckman has, however, very kindly examined this specimen, 

 and, in a letter to the writer, says: "It would be advisable to ascribe 



it to Dorsetensia Its costation indicates either Grammoceras 



or one of the Sonninince ; its septation— the tridactyloid character of 



